Transmission apparatus and method for MIMO system

ABSTRACT

A transmitter in a multiple input multiple output (MIMO) communication system is provided. The transmitter includes a multiplexer for multiplexing an input bit stream into a plurality of bit streams, and outputting the bit streams in parallel; a bit-order rearranger for reordering bits constituting the bit streams, which are output from the multiplexer in the same time period, and outputting the reordered bits as reordered bit streams; and a modulator for modulating the parallel reordered bit streams output from the bit-order rearranger according to their associated modulation schemes, and transmitting the modulated symbols via their associated antennas.

PRIORITY

This application claims the benefit under 35 U.S.C. § 119(a) of an application entitled “Transmission Scheme for MIMO System” filed in the Korean Intellectual Property Office on Feb. 2, 2005 and assigned Serial No. 2005-9561, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a wireless communication system, and in particular, to a transmission scheme for a Multiple Input Multiple Output (MIMO) communication system.

2. Description of the Related Art

In a MIMO communication system that transmits/receives data using a plurality of transmission antennas and reception antennas, a MIMO channel formed by the transmission and reception antennas is disassembled into a plurality of independent spatial channels. Each of the spatial channels is mapped to one dimension, and the use of additional dimensions created by the multiple transmission and reception antennas improves performance of the MIMO system.

In a wireless communication system, transmission data forms a symbol stream through a coding and modulation process, and the symbol stream is phase-shifted into a radio frequency (RF) modulated signal that is suitable to be transmitted over a wireless channel.

A data transmission scheme using the MIMO system is classified into a Spatial Multiplexing (SM) scheme and a Spatial Diversity (SD) scheme. The SM scheme simultaneously transmits different data using multiple transmission antennas, thereby transmitting data at a high rate without increasing a bandwidth of the system. The SD scheme transmits single data stream via multiple transmission antennas, thereby obtaining transmit diversity gain.

FIG. 1 is a block diagram illustrating a structure of a transmitter based on a Bell Labs LAyered Space-Time (BLAST) scheme, which is the conventional SM scheme. An input bit stream is multiplexed into four parallel bit streams S₁, S₂, S₃ and S₄ by a multiplexer (MUX) 101. The individual bit streams S₁, S₂, S₃ and S₄ are modulated into modulation symbols X₁, X₂, X₃ and X₄ according to a modulation technique of their associated modulators 103, and then transmitted through four associated transmission antennas. In this case, the modulation technique is a quadrature phase shift keying (QPSK) scheme. In the BLAST scheme, multiplexing gain is in proportion to the number of transmission antennas and reception antennas. However, the BLAST scheme, as it provides no diversity gain, there is a decrease in bit error rate (BER) performance in a high signal-to-noise ratio (SNR) environment, and it suffers an abrupt change in performance depending on the type of receiver and transmission optimization technique.

FIG. 2 is a block diagram illustrating a structure of a transmitter based on a Double Space-Time Transmit Diversity (DSTTD) scheme, which is the conventional SD scheme. Modulation symbols X₁, X₂, X₃ and X₄ modulated through the process of FIG. 1 are pre-coded by a transmission matrix of a pre-encoder 105 before being transmitted. The transmission matrix has a form defined by Equation (1): $\begin{matrix} {B = \begin{bmatrix} x_{1} & x_{2} & x_{5} & x_{6} \\ x_{2}^{*} & {- x_{1}^{*}} & x_{6}^{*} & {- x_{5}^{*}} \\ x_{3} & x_{4} & x_{7} & x_{8} \\ x_{4}^{*} & {- x_{3}^{*}} & x_{8}^{*} & {- x_{7}^{*}} \end{bmatrix}} & (1) \end{matrix}$

The DSTTD scheme using the 4×4 transmission matrix shown in Equation 1 has both a multiplexing gain of 2 and a diversity gain of 2, thus contributing to performance improvement, but results in a decrease in data rate due to the reduction in the multiplexing gain.

For improvement in system performance, the MIMO system has recently been designed so as to support at least one of the SM techniques and the SD techniques. In this scheme, a particular transmission technique is selected in a given time period according to channel conditions and required results.

However, because a transmission technique for spatial multiplexing and a transmission technique for spatial diversity are different from each other in design, supporting both of the transmission techniques for spatial multiplexing and spatial diversity within one system causes an increase in complexity of transceivers.

SUMMARY OF THE INVENTION

The present invention is provided to substantially solve at least the above problems and/or disadvantages. It is, therefore, an object of the present invention to provide a transmission apparatus and method for improving multiplexing gain while maintaining the diversity gain available in the conventional spatial diversity technique, through a simple coding process.

It is another object of the present invention to provide a transmission apparatus and method for adjusting diversity gain through modification of a bit/symbol mapping pattern.

It is further another object of the present invention to provide a transmission apparatus and method for improving multiplexing gain and adjusting diversity gain without increasing complexity of a decoder.

It is still another object of the present invention to provide a transmission apparatus and method for maximizing system performance by adjusting multiplexing gain and diversity gain according to environment, without increasing complexity.

According to one aspect of the present invention, there is provided a transmitter in a multiple input multiple output (MIMO) communication system. The transmitter includes a multiplexer for multiplexing an input bit stream into a plurality of bit streams, and outputting the bit streams in parallel; a bit-order rearranger for reordering bits constituting the bit streams, which are output from the multiplexer in the same time period, and outputting the reordered bits as reordered bit streams; and a modulator for modulating the parallel reordered bit streams output from the bit-order rearranger according to their associated modulation schemes, and transmitting the modulated symbols via their associated antennas.

According to another aspect of the present invention, there is provided a transmission method in a multiple input multiple output (MIMO) communication system. The method includes multiplexing a serial input bit stream into parallel symbols, which are output in the same time period; generating reordered bit streams by reordering bits constituting the parallel output symbols; and modulating the reordered bit streams according to their associated modulation schemes, and simultaneously transmitting the modulated symbols via their associated antennas.

According to further another aspect of the present invention, there is provided a transmission method in a multiple input multiple output (MIMO) communication system. The method includes multiplexing a serial input bit stream and outputting four symbols in the same time period; mapping the four symbols in units of two symbols; generating four reordered bit streams by reordering bits constituting the reordered bit streams; and modulating the generated four reordered bit streams according to their associated modulation schemes and simultaneously transmitting the modulated symbols via their associated transmission antennas.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram illustrating a structure of a transmitter based on a Bell Labs Layered Space-Time (BLAST) scheme which is the conventional spatial multiplexing scheme;

FIG. 2 is a block diagram illustrating a structure of a transmitter based on a Double Space-Time Transmit Diversity (DSTTD) scheme which is the conventional spatial diversity scheme; and

FIG. 3 is a block diagram illustrating a structure of a Multiple Input Multiple Output (MIMO) transmitter according to the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT

A MIMO transmission apparatus and method according to the present invention will now be described with reference to the accompanying drawings.

FIG. 3 is a block diagram illustrating a structure of a MIMO transmission apparatus according to the present invention. As illustrated in FIG. 3, a MIMO transmission apparatus according to the present invention includes a multiplexer 301 for multiplexing an input bit stream b₁, b₂, b₃, b₄, . . . into a plurality of parallel bit streams S₁, S₂, S₃, and S₄, a bit-order rearranger 303 for reordering bits constituting the parallel bit streams into a plurality of reordered bit streams M₁, M₂, M₃, and M₄, and a plurality of modulation modules 305 for modulating the reordered bit streams M₁, M₂, M₃, and M₄ into transmission symbols X₁, X₂, X₃ and X₄ using a predetermined modulation technique and transmitting the transmission symbols X₁, X₂, X₃ and X₄ via their associated transmission antennas. The transmission symbols X₁, X₂, X₃ and X₄ may be pre-coded through a transmission matrix before being transmitted. Preferably, the modulation technique utilized by the present invention is a 16-ary Quadrature Amplitude Modulation (16 QAM) scheme.

Herein, it will be assumed for illustration purposes that the number Nt of transmission antennas is 4 (N_(t)=4).

Upon receiving the input bit stream b₁, b₂, b₃, b₄, . . . , the multiplexer 301 generates four parallel bit streams S₁, S₂, S₃ and S₄ by processing the input bit stream b₁, b₂, b₃, b₄, . . . in units of 8 bits. Each of the generated symbols includes two bits. In other words, bit stream S₁ represents input bits b₁ and b₂, bit stream S₂ represents input bits b₃ and b₄, bit stream S₃ represents input bits b₅ and b₆, and bit stream S₄ represents input bits b₇ and b₈. The generated bit streams S₁, S₂, S₃ and S₄ are input in parallel to the bit-order rearranger 303, and the bit-order rearranger 303 generates reordered bit streams M₁, M₂, M₃ and M₄, the number of which is equal to the number of its input bit streams S₁, S₂, S₃ and S₄, by performing mapped-reordering on the bits constituting the bit streams S₁, S₂, S₃ and S₄. In the bit reordering process, a first reordered bit stream M₁ is configured by sequentially ordering the input bits b₁ and b₂ constituting the first bit stream S₁ and the input bits b₅ and b₆ constituting the third bit stream S₃. A second reordered bit stream M₂ is configured by sequentially ordering the input bits b₃ and b₄ constituting the second bit stream S₂ and the input bits b₇ and b₈ constituting the fourth bit stream S₄. Similarly, a third reordered bit stream M₃ is configured by sequentially ordering the input bits b₅ and b₆ constituting the third bit stream S₃ and the input bits b₁ and b₂ constituting the first bit stream S₁, and a fourth reordered bit stream M₄ is configured by sequentially ordering the input bits b₇ and b₈ constituting the fourth bit stream S₄ and the input bits b₃ and b₄ constituting the second bit stream S₂. In conclusion, the reordered bit streams M₁, M₂, M₃ and M₄ have bit streams of M₁=b₁b₂b₅b₆, M₂=b₃b₄b₇b₈, M₃=b₅b₆b₁b₂, and M₄=b₇b₈b₃b₄, respectively. The configured reordered bit streams M₁, M₂, M₃ and M₄ are input to the modulator 305, and modulation modules constituting the modulator 305 modulate the reordered bit streams M₁, M₂, M₃ and M₄ into transmission symbols X₁, X₂, X₃ and X₄ using a 16-ary Quadrature Amplitude Modulation (16 QAM) scheme and transmit the transmission symbols X₁, X₂, X₃ and X₄ via their associated transmission antennas.

Although each of the reordered bit streams is created herein by sequentially ordering bits constituting two different bit streams, the number of bits constituting a bit stream, the number of bits copied from a bit stream, the number of bits constituting a reordered bit stream, the number of bit streams, from each of which bits constituting a reordered bit stream are to be copied, and the ordering sequence of the copied bit streams are subject to change according to system environment, and the change causes a change in diversity gain and data rate.

In addition, although 16 QAM is used herein as a modulation scheme, the embodiment of the present invention is not limited to this, and can also be applied to various modulation schemes, such as Quadrature Phase Shift Keying (QPSK) or 64 QAM.

As can be understood from the foregoing description, the novel data transmission apparatus and method can improve diversity gain while maintaining a data rate available in the conventional spatial multiplexing transmission scheme and can also increase a data rate while maintaining diversity gain available in the conventional spatial diversity transmission scheme, through a simple coding process using bit-order rearranging.

In addition, the novel data transmission apparatus and method can adjust multiplexing gain and diversity gain according to required system conditions without increasing system implementation complexity, thereby maximizing system performance.

While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 

1. A transmitter in a multiple input multiple output (MIMO) communication system having multiple antennas, the transmitter comprising: a multiplexer for multiplexing an input bit stream into a plurality of bit streams, and outputting the bit streams in parallel; a bit-order rearranger for reordering bits constituting the bit streams, which are output from the multiplexer in the same time period, and outputting the reordered bits as reordered bit streams; and a modulator for modulating the parallel reordered bit streams output from the bit-order rearranger so as to generate symbols according to their associated modulation schemes, and transmitting the symbols via their associated antennas.
 2. The transmitter of claim 1, wherein the bit-order rearranger selects the bit streams which are output from the multiplexer in the same time period, in units of at least two bit streams, and reorders all bits constituting the selected bit streams in a predetermined order.
 3. The transmitter of claim 1, wherein the bit-order rearranger selects the bit streams which are output from the multiplexer in the same time period, in units of at least two bit streams, selects at least one bit in a predetermined bit position among bits constituting each of the selected bit streams, and reorders the selected bits.
 4. A transmission method in a multiple input multiple output (MIMO) communication system, the method comprising the steps of: multiplexing a serial input bit stream into parallel bit streams, which are output in the same time period; generating reordered bit streams by reordering bits constituting the parallel bit streams; and modulating the reordered bit streams according to their associated modulation schemes so as to generate symbols, and simultaneously transmitting the symbols via their associated antennas.
 5. The transmission method of claim 4, wherein the generating step comprises: selecting the parallel bit streams in units of at least two bit streams; and reordering all bits constituting the selected bit streams.
 6. The transmission method of claim 4, wherein the generating step comprises: selecting the parallel bit streams in units of at least two bit streams; copying at least two bits among the bits constituting each of the selected bit streams; and reordering the copied bits in a predetermined order.
 7. The transmission method of claim 6, wherein the number of the reordered bit streams is equal to the number of the parallel modulated symbols.
 8. The transmission method of claim 4, wherein the generating step comprises: selecting the parallel bit streams in units of at least two bit streams; copying at least one bit in a predetermined bit position among the bits constituting each of the selected bit streams; and reordering the copied bits in a predetermined order.
 9. A transmission method in a multiple input multiple output (MIMO) communication system, the method comprising the steps of: multiplexing a serial input bit stream and outputting four bit streams in the same time period; selecting the four bit streams in units of two bit streams; generating four reordered bit streams by reordering bits constituting the bit streams; and modulating the four reordered bit streams into symbols according to their associated modulation schemes and simultaneously transmitting the symbols via their associated transmission antennas.
 10. The transmission method of claim 9, wherein each of the symbols comprises at least two bits.
 11. The transmission method of claim 10, wherein the generating step comprises: copying at least two bits among the bits constituting each of the bit streams; and reordering the copied bits in a predetermined order.
 12. The transmission method of claim 10, wherein the generating step comprises: copying at least two bits in particular bit positions of the bit streams; and reordering the copied bits in a predetermined order. 